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Who has the most web servers? One of the leaders was 1&1 Internet. This is its data center in Karlsruhe, Germany.

It's time to take a look back at the best and worst of 2009. We start today with a look at the most popular articles published on Data Center Knowledge in 2009, as determined by our readers. These were the stories that attracted the most page views during the year:

Who Has The Most Web Servers?Topping the list is our look at the companies with the most servers in their data centers, according to public data, as well as some speculation about the "secret servers" at Google, Microsoft and elsewhere.

The Gallery of Exploding Servers: Some servers die quietly in their racks, with little fanfare. But not these servers. Some failed to meet expectations. Others were found to be convenient fodder for marketing stunts. All of them had their violent demise preserved on video and posted on the Internet.

Facebook Now Has 30,000 Servers: The relentless growth of Facebook fueled a number of our stories this year. News that the social network has crossed the 30,000 server barrier seemed to catch the imagination of our readers.

Inside the 'James Bond Villain' Data Center: How can you not love an underground data bunker 100 feet below Stockholm, complete with waterfalls, greenhouse-style NOC, glass-enclosed conference room “floating” above the colocation floor, and blue-lit diesel engines? Dean Nelson of Data Center Pulse took the tour, and we lived vicariously through the video.

Google's Chiller-Less Data Center: Data center operators have been moving away from the use of energy-hungry chillers to cool their data centers. And no one moved further than Google, which built its new data center in Belgium with no chillers on-site.

How Google Routes Around Outages: Making changes to Google’s search infrastructure is akin to “changing the tires on a car while you’re going at 60 down the freeway,” according Urs Holzle, who oversees the company’s massive data center operations.

Inside Microsoft's Dublin Mega Data Center: A closer look at Microsoft's Dublin facility, which represents a milestone in data center design. The new data center will power much of Microsoft’s global cloud computing operation, while using far less energy and water than typically consumed in other data centers of this scale.

HP Scales Out With New Cloud Servers: In a departure from its "blade everything" reputation, HP launched a line of rackmount servers designed to appeal to cloud-builders’ focus on energy efficiency and cost, and be delivered by the rackload.

Google Unveils its Container Data Center: After years of secrecy, Google lifted the lid on its data center operations during an April summit for industry executives. The highlight of the day was a video tour of the long-rumored container data center, which was built in 2005 - confirming that Google was into containers before containers were cool.

Google Envisions 10 Million Servers: There were many data center innovators in 2009, but Google continues to prompt fascination from Internet watchers. That included our summary of a presentation by a Google engineer indicating that the company is preparing to manage as many as 10 million servers in the future.